Refractory article and production process thereof

Abstract

The present invention relates to refractory articles in general having improved surface properties. The objective of the invention is to propose an improvement of the refractory articles comprised of a fused silica matrix which will overcome the some of the defects while keeping the excellent known properties of the fused silica matrix. This objective is reached when a sintered ceramic phase is present in the porosity of at least a portion of at least a surface of the matrix. The present invention also relates to a process for producing such an article.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is based on and claims priority under 35 U.S.C. 119 from EP06113994.5, filed May 16, 2006, and is the national phase under 35 U.S.C. §371 of PCT / EP / 2007 / 004248, filed May 14, 2007.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not ApplicableTHE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT[0003]Not ApplicableINCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC[0004]Not ApplicableSEQUENCE LISTING[0005]Not ApplicableBACKGROUND OF THE INVENTION[0006]1. Field of the Invention[0007]The present invention relates to refractory articles in general having improved surface properties. In particular, it relates to refractory articles comprised of a fused silica matrix such as rollers for conveying hot articles or articles used for the treatment of molten glass or non-ferrous metals such as crucibles for melting or crystallizing silicon, rotary degasser for the treatment of aluminum, etc.[0008]2. ...

AI Technical Summary

Benefits of technology

The invention involves a method for improving the properties of a fused silica article by filling in its surface with silica to prevent cracking and ensure material continuity. The filler is homogeneously dispersed on the surface layer and contributes synergistically to significantly improve the article's performance. The process results in a reduced surface porosity and pore size, as well as a smoother surface texture and improved flexural strength. No further machining steps are required after the impregnation step.

Problems solved by technology

Certain surface properties of the fused silica materials however make them unsuitable for some applications.

In particular, the “surface pickup” behavior (inclination of the material to pick up impurities or fragments present at the surface of the transported article) or the “surface buildup” behavior (inclination of the surface to receive and accumulate metallic particles (such as tin, silicon, etc.) possibly oxidized (tin oxide)) renders quite problematic their use as glass annealing rolls (LOR, Lehr), as glass tempering rolls (GTR) or as containers for handling and / or treating molten glass or metal (e.g. crucible for melting silicon).

Marking of the transported articles and adhesion of the silicon crystal to the walls of the crucible are examples of such problems.

For such applications, it is necessary either to provide the silica matrix with an expensive and elaborated coating or to use another material (such as metal).

In both cases, the sprayed or patched material is added on top of the existing blocks surface so that the final surface is rough and hardly controllable.

Furthermore, possible oxidation in temperature for the SiAlON and irreversible crystallization of the fused silica makes the SiAlON material unsuitable for thermal cycling applications.

In addition, the provision of a coating is always expensive since it requires additional production steps and further, is only a temporary solution since, unavoidably, the further layer of the coating material has a tendency to delaminate from the surface of the silica matrix material which not only deprives the fused silica material from the benefit of the coating but in turn produces scaling defects.

Further, since the thermal expansion (or the thermal behavior in general) of this further layer is different from the thermal expansion (or the thermal behavior in general) of the silica matrix, constraints are generated at the interface between the coating and the silica matrix, affecting thereby negatively the surface quality.

Moreover, since the thermal conductivity of this further layer is not the same as the thermal conductivity of the fused silica matrix, the transfer of heat through the article is not homogeneous.

The use of metallic materials for such articles is also unsatisfactory since metals have a relatively high reactivity towards the treated or transported articles.

In addition, metallic articles have a quite high flexural deformation with comparison to fused silica articles and their efficient time of use in a heavy environment (such as a Lehr or a crystallization furnace) is relatively short.